Punctuated Equilibrium and the Validation of Macroevolutionary Theory 911
This recasting of human evolution in speciational terms documents the extent
of proffered revision, but the scope of reform gains even greater clarity when we
recognize the pervasive nature of the speciational theme as a guide for resolving
paradoxes, understanding puzzles of popular misconception, and offering new
formulations to break impasses in almost every nook and cranny of discussion
about the evolutionary history of our own lineage. When common claims seem
askew or confused, I would venture to suggest that the first and best strategy for
breakthrough will usually lie in a speciational reformulation for any puzzling issue.
Consider just three bugbears of popular confusion in serious newspapers and
magazines, and in books on general science for lay audiences, all finding a
potentially simple and elegant resolution in speciational terms.
- The ordinariness of "out of Africa." During the 1990's, popular articles on
human evolution, at least in American media, focussed upon one issue above all
others: the supposed dichotomy between two models for the origin of Homo
sapiens. The press labelled these alternatives as, first, the "multiregional"
hypothesis (also dubbed the "candelabra" or the "menorah" scheme to honor our
religious pluralism in metaphorical choice) representing the claim that Homo
erectus migrated from Africa about 1.5 to 2.0 million years ago and established
populations on the three continents of Africa, Europe, and Asia. All three subunits
then evolved in parallel (with enough gene flow to maintain cohesion) towards
more gracile and substantially bigger-brained Homo sapiens. The second position,
usually called "out of Africa" or "Noah's ark," holds that Homo sapiens emerged in
one coherent place (presumably Africa from genetic evidence of relative
similarities among modern humans) as a small, speciating population
geographically isolated from the ancestral Homo erectus stock. This new species,
probably arising less than 200,000 years ago, then migrated out of Africa to spread
throughout the habitable world, displacing, or perhaps partly amalgamating with,
any surviving stocks of Homo erectus encountered along the way.
The dichotomous division, as presented by the media, may have been a bit
stark and unsubtly formulated. But I can raise no major objection either to the basic
categorization or to most press reports about details of explanation and evidence.
Still, I became more and more puzzled, and eventually amused in a quizzical or
sardonic way, by a remarkable fallacy in basic interpretation that pervaded
virtually every article on the subject. Almost invariably, popular presentations
labelled the multiregional view as the conventional expectation of evolutionary
theory, and out-of-Africa as astonishingly iconoclastic, if not revolutionary.
But all professionals must recognize that the exactly opposite situation
prevails. Out-of-Africa presents a particular account, "customized" for human
evolution, of the most ordinary of all macroevolutionary events—the origin of a
new species from an isolated, geographically restricted population branching off
from an ancestral range, and then, if successful, spreading to other suitable and
accessible regions of the globe. By contrast, multiregionalism should be labelled as
iconoclastic, if not a bit bizarre. How could a new species evolve in lockstep
parallelism from three ancestral populations spread